Don't have samples to hand, nor wedding experience...
I have both the Rokinon and Sigma 8mm, shooting canon crop sensors. These are two very different lenses.
Not only is there a massive difference in the coatings and quality of the images, which is important with ultrawide to fisheye, because there *will* be light sources in your shots, but the geometry of the image is waaay different. The Rokinon is more of an ultrawide look, with more of the wide-angle distortion that is visible in in the 11 to 16 mm range on crop. In other words, it attempts to correct towards rectilinear. And fails to get to it, of course.
The Sigma is more of a classic fisheye with a round image on a full frame camera, but on crop is cropped in to have the edges of the circle nearly touch the edges of the the frame left and right, which means that the top and bottom of the circle is cut off at the edge of the frame. And of course the image quality is noticeably better, without the severe flares of the Rokinon.
I like both these lenses for different reasons, but if I had to have just one, it would be the Sigma!
I'm still a relative newbie here, guess it's time to learn about embedding images or links in posts... Seems to me I should have some Sigma images accessible...
Edit: Ah, here we go. Examples of the Sigma 8mm on a Canon 60D. No post cropping.
Here's an example with people.
Note just how close the camera is to the subjects - I have short arms!
Here's a landscape.
To keep a horizontal line relatively unbowed, it needs to be near the center of the image.
PS. The Rokinon is manual iris on the lens, and manual focus. The Sigma has body control of iris, and MF/AF.
From the upper left corner of the U.S.
Photos, Video & Pano r us.
College and workshop instructor in video and audio.
70D, Sigma 8mm, Tokina f2.8 11-16, Canon EF-S f2.8 17-55, Sigma f2.8 50-150 EX OS, Tamron 150-600VC. Gigapan Epic Pro, Nodal Ninja 5 & R10.